Camera projections can be modeled in various ways, e.g., as a pinhole camera model, a “thick lens” or “thin lens” model, a fisheye lens model, etc., with and without consideration of lens errors and lens distortions. All of the models have in common that the projection can be described by so-called camera projection parameters that directly form, e.g., in simplified models, the coefficients of a geometric projection matrix.
The use of a direct linear transformation (DLT) for determining camera projection parameters has been known for a long time, as referenced, for example, in Abdel-Aziz, Y. I., and Karara, H. M.: “Direct Linear Transformation from Comparator Coordinates into Object Space Coordinates in Close-range Photogrammetry,” Proceedings of the Symposium on Close-Range Photogrammetry, pp. 1-18, 1971, Falls Church, Va., American Society of Photogrammetry. For the use of DLT for determining camera projection parameters, the knowledge of at least six points spanning the space in the viewing space, so-called “world points,” and their allocation to image points in the camera image are required. For this purpose, according to current prior art, at least six markings must be arranged distributed in the entire viewing space of the camera and then allocated to the correct image points in the camera image.
For traffic-monitoring cameras for underpasses or highways, wherein these cameras can have a large viewing field of up to several hundred meters, this means large time costs, because the individual markings must be placed, e.g., by hand on the street and measured relative to each other by means of laser-ranging meters or measuring chains. For this purpose, as a rule, a blockage of the tunnel or the section of the street is necessary, which is extremely obstructive: even for tunnel cameras, frequent recalibration of the monitoring cameras is necessary, because these can be moved during the regular washing of the tunnel or due to collisions with trucks driving past. The camera must also be recalibrated each time it is repaired or serviced.